Query Processing and its performance is the heart of any RDBMS. SAP ASE uses cost based optimizer for query processing and optimization means it creates the different access path (query plan) for a query and it picks up best plan which has least cost for a given query. This query plan cost is calculated from the data distribution and statistics information of a table and its columns.

There are two types of statistics –

Object Level Stats : The object level statistics describe a table and its indexes and include values such as number of rows and pages in the table and/or index (es), the number of empty pages, and the cluster ratios among others. Some of the object level statistics are updated automatically by ASE, others when ‘update statistics’ is run.

Column Level Stats : The column level statistics describe the distribution of values in the column; they consist of the column’s histogram and density values and are updated when an index is created or an ‘update statistics’ command is run.

System Tables which store these stats:

The systabstats and sysstatistics tables store statistics for all tables, indexes, and any un-indexed columns for which you have explicitly created statistics.

systabstats stores information about the table or index as an object, and is updated by query processing, data definition language, and update statistics commands. Simply it stores object level of statistics.These statistics include:

Number of data pages for a table, or the number of leaf level pages for an index.

Number of rows in the table

Height of the index

Average length of data rows and leaf rows

Number of forwarded and deleted rows

Number of empty pages

Statistics to increase the accuracy of I/O cost estimates, including cluster ratios, the number of pages that share an extent with an allocation page, and the number of OAM and allocation pages used for the object

Stopping points for the reorg command so that it can resume processing

systabstats contains one row for each clustered index, one row for each nonclustered index, one row for each table without a clustered index, and one row for each partition.

The storage for clustered index information depends on the locking scheme for the table:

For data-only-locked tables, systabstats stores an additional row for a clustered index.

For allpages-locked tables, the data pages are treated as the leaf level of the index, so the systabstats entry for a clustered index is stored in the same row as the table data.The indid column for clustered indexes on allpages-locked tables is always 1.

sysstatistics table stores one or more rows for each indexed column on a user table; it also stores statistics for unindexed columns.

The first row for each column stores basic statistics about the column, such as the density for joins and search arguments, the selectivity for some operators, and the number of steps stored in the histogram for the column.

If the index has multiple columns, or if you specify multiple columns when you generate statistics for unindexed columns, there is a row for each prefix subset of columns.

Additional rows store histogram data for the leading column. Histograms do not exist if indexes were created before any data was inserted into a table. To generate a histogram, run update statistics after inserting data.

Scalability, speed, security, simplicity…these were the guiding principles for our engineers. We’ve increased scalability and speed with extensive optimization in its transaction concurrency management, query plan execution, data compression and utilization of computing resources in large SMP servers. Security enforcement and system auditability have been augmented to provide customers more flexibility to adapt to their specific regulatory compliance needs. And SAP Control Center delivers simplified database management helping to reduce overall cost of ownership.

Sqsh (pronounced skwish) is short for SQshelL (pronounced s-q-shell), it is intended as a replacement for the venerable ‘isql’ program supplied by Sybase.

Sqsh is much more than a nice prompt, it is intended to provide much of the functionality provided by a good shell, such as variables, aliasing, redirection, pipes,back-grounding, job control, history, command substitu-tion, and dynamic configuration. Also, as a by-product of the design, it is remarkably easy to extend and add functionality.

Sqsh was developped by Scott C. Gray, and is currently maintained by Michael Peppler (mpeppler@peppler.org) and also by Martin Wesdorp (mwesdorp@users.sourceforge.net).

Transaction T1 (Session 1)modifies a data item. Another transaction T2 (Session 2)then reads that data item before T1 performs a COMMIT or ROLLBACK. If T1 then performs a ROLLBACK, T2 has read a data item that was never committed and so never really existed.

Now with isolation level 0 , I am trying to read data and it is allowing dirty reads.

rollback

If Session 1 rollbacks, session will have inconsistent.

Understanding Isolation Level “2” : Avoid Repeatable Reads

What is Repeatable Reads?

Transaction T1 (session 1) reads a data item. Another transaction T2 (session 2) then modifies or deletes that data item and commits. If T1 then attempts to reread the data item, it receives a modified value or discovers that the data item has been deleted.

Transaction T1 reads a set of data items satisfying some . Transaction T2 then creates data items that satisfy T1’s and commits. If T1 then repeats its read with the same , it gets a set of data items different from the first read.

SAP

Located in Walldorf, Germany, SAP (www.sap.com) has several DBMS products that are used for transaction systems: SAP Sybase Adaptive Server Enterprise (ASE), SAP Sybase iAnywhere and SAP Hana. Both ASE and iAnywhere are available as software only, while SAP Hana is marketed as an appliance.

In less than 18 months since the offering’s release in April 2012, more than 1,000 customers have chosen to run SAP Business Suite on SAP Sybase ASE and there are more than 2,000 customer installations. Both new and existing SAP customers can run a high-performance relational database management system (RDBMS) optimized for SAP Business Suite that helps improve operational efficiency and significantly reduce overall costs. The announcement was made at the SAP Database and Technology Partner Summit in Barcelona.

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Anurag has more than 6+ years of experience in Sybase Database Development .His Area of expertise includes Performance, Query Optimization, Cost Optimization, TSQL Development. He is also involved in Consultancy to Financial Firms for Database Implementation and Maintenance. He has supported many Global Financial firms and recently started a new portal -Mati Rang. AnVa (Founder) has more than 6+ years Exp in Sybase ASE/REP Database Administration. His area of interest is ASE Implemenation and maintenance , Performace Tunning , Sybase HA ,Shared Cluster and Replication. Also exploring the In-Memory Databases (HANA) , Big Data, Hadoop and Java. He is also supporting the Forum Sybase Team and started this sybaseblog.com in late 2009.Andrew is Guest Blogger on sybaseblog.com. Andrew have been working with Sybase for more than a decade: ASE & RS mostly.
He has written lot of tools that help to manage/monitor the system for ASE and Replication and some tools are on the way..
He is also poet and love to be creative all the way.

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